The Arduino Inventor's Guide (52 page)

Solder, shown in
Figure A-4
, is a metal alloy with a relatively low melting temperature. Modern solder melts at a temperature of around 180 degrees Celsius or 356 degrees Fahrenheit, about the temperature you need to bake cookies. Most solder used for electronics has a core of
flux
, a cleaning fluid. As the solder melts, the flux helps to clean the surfaces being soldered and helps the solder flow.

FIGURE A-4:
A roll of solder

To perform soldering, you use a
soldering iron
. Most soldering irons are about the size of a medium carrot and have two main parts: the handle and the hot end (see
Figure A-5
).

FIGURE A-5:
A typical soldering iron

There are many styles and types of soldering irons. Lower-cost irons can be about $10 and usually have a fixed temperature setting, but we suggest getting an iron with some type of temperature adjustment knob. The optimal temperature for an iron is about 650 degrees Fahrenheit. If it’s too hot, the tip will oxidize and get dirty quickly. If it’s not hot enough, it won’t melt the solder. An adjustable iron will help you control this, so it’s worth spending a little extra.

Be very careful when using a soldering iron: when you turn it on, the hot end will very quickly get hot enough to melt metal. That’s really hot! Always hold a soldering iron from the handle—you should never hold it from the hot end even when it’s off.

You should also protect the table surface you’re working on with a piece of cardboard, a cutting mat, or scrap piece of wood. And, before you start soldering, you should always wear eye protection. Little bits of solder and flux do sometimes sputter off. It’s best to keep your precious eyes safe!

To use a soldering iron, first plug in your iron and let it heat up. Depending on the type of iron you have, this may take anywhere between 30 seconds and a couple of minutes. While the iron is heating up, make sure it’s resting on a stand so that the hot end is not touching your table or work surface.

When the iron is hot, the solder should melt easily, so test this by touching a piece of solder with the side of the iron’s tip. This is the hottest part of the iron, known as the
sweet spot
(shown in
Figure A-6
), and it is the part you should use to apply heat to components. If the solder melts immediately, your iron is hot enough to solder.

FIGURE A-6:
The side of the tip is much hotter than the very end of the tip.

Contrary to what you might assume, when soldering you don’t actually touch the iron directly to the solder to melt it. The trick is to hold the iron to the components you’re intending to solder for around 2 to 3 seconds. Then you apply solder directly to the heated joint, and the solder will melt. Solder will always flow toward the heat and settle in the hottest part of the component. If you feed the solder directly onto the iron, it may glob up on the iron and not go onto the parts you want to solder. If this happens, simply clean the iron and try again. Hold the iron the same way you would hold a pencil, with your dominant hand, holding it from the handle. With your other hand, hold a length of solder. Be careful not to hold the solder too close to the end you’re melting, as the heat may travel up the length of solder to your fingertips.

Touch the sweet spot of the iron to the parts that you intend to solder. Be sure that the sweet spot of the iron is touching both parts that need to be soldered so that they heat up equally, as shown in
Figure A-3
. Count for three full seconds: one one-thousand, two one-thousand, three one-thousand.

Next, while holding the iron to the components, feed the end of the solder into the joint. Remember, the solder will flow toward the heat.

After you have fed enough solder so that the joint is filled, remove the solder, but hold the iron in place for one more second. This will allow the solder to flow and settle. Remove the iron from the joint, and place it back onto its stand.

A good solder joint should be smooth and somewhat shiny. If you’re soldering onto a PCB, the joint often resembles a small volcano or chocolate candy kiss. Soldering takes practice, so if your solder joint doesn’t look clean and smooth, try reheating the joint to get the solder to flow and settle again, or add a bit more solder.
Figure A-7
illustrates some common mistakes and possible solutions for soldering.

FIGURE A-7:
Common soldering mistakes and solutions

Keeping the tip of the iron clean is one of the secrets to getting a good solder joint. We recommend cleaning it before each use by heating it up and using a brass scrubber or wet sponge to wipe off any excess solder and oxidation that may have built up.

If the tip is dirty and you can’t wipe off the excess buildup, you can use Tip Tinner and Cleaner (TOL-13246); this is a mixture of a mild acid and solder. To clean with this, heat the iron, place the tip of the hot iron into the tip tinner, and let the tip tinner eat away at the oxidation and buildup for about 10 to 15 seconds at a time. Then, wipe the tip off on the sponge. Repeat this process if necessary. The tip of the iron should be shiny.

Figure A-8
shows a few additional hints and suggestions for using the soldering iron.

FIGURE A-8:
Soldering hints and suggestions

Using a soldering iron is a skill that should be in any maker’s arsenal. When you’re ready to make your prototype projects more permanent and durable, soldering will ensure that the wires and connections between components don’t get disconnected.

Here are a few additional tools we’d recommend you use to help you make the perfect solder joint each time. These tools help hold your parts, clean up your solder joints, and remove extra solder.

A
third hand
is basically a clamp to hold down the pieces you’re soldering and will be one of your best helpers for soldering. There are many versions of third hands, but most are simply a couple alligator clips on a heavy stand that will hold your parts while you’re using your hands to hold the solder and the iron. Many of the basic ones even come with a magnifying glass and a small soldering iron stand, too, as shown in
Figure A-9
.

FIGURE A-9:
Third hand soldering stand

One of the tricks to getting a good solder joint is to make sure everything is clean, which you can do with flux, a slightly acidic cleaning fluid often made from tree rosin. A flux pen (see
Figure A-10
) works a lot like a paint marker; you simply press the tip of the marker down on the solder joint you’re working on until a small puddle of liquid comes out onto your board. Apply the soldering iron directly to the joint and insert the solder and, using flux, the solder will melt a lot faster and bond better to your components.